The present embodiments relate to an adaptive X-ray filter for varying the local intensity of X-ray radiation.
When examinations are carried out using X-rays, a patient or the patient's organs may exhibit a widely differing absorption behavior in a region under examination with respect to the applied X-ray radiation. For example, in the case of thorax X-rays, the attenuation in the mediastinum (e.g., the region in front of the lobes of the lungs) is very high as a result of the organs located there. In contrast, the attenuation is very low in the region of the lobes of the lungs itself. Both in order to obtain a meaningful X-ray image, and to protect the patient, the applied dose may be set on a region-specific basis such that no more X-ray radiation is delivered than is necessary. In those regions with high attenuation, a greater X-ray radiation dose is to be applied than in regions with lower attenuation. In addition, there are applications in which only one part of the examined region is to be X-rayed with high diagnostic quality (e.g., with less noise). The surrounding parts may be important for orientation but not for the actual diagnostic process. These surrounding regions may therefore be imaged at a lower dose in order to reduce the overall dose applied.
With regard to certain X-ray examinations, variations in the thickness of the human body are compensated for, and thus, the uniformity of the radiation is increased for imaging purposes. This may be achieved by a filter that is designed such that the material thickness thereof may be varied continuously or stepwise in order to thereby enable adjustment of the intensity distribution of the X-ray radiation.
During an X-ray examination skin-damaging soft and medium-soft rays are also produced. The skin-damaging soft and medium-soft rays may have only minor diagnostic relevance because the soft and medium-soft rays are in large part absorbed by the tissue of the patient and do not arrive at the image receptor. For this reason, the radiation is to be “hardened”. This provides that the softer rays (e.g., longer wavelength less penetrating rays) are to be filtered out by an X-ray filter.
German patent specification DE 196 38 621 C1 describes a filter that may be adjusted on a region-specific basis for absorbing X-ray radiation. The adjustability is provided by a controllable matrix arranged on a housing for generating a field acting on a liquid contained in the housing. The housing includes at least two chambers that are separated from one another in a sealed manner by a flexible membrane. The chambers contain liquids differing in absorption behavior for X-rays. At least one of the liquids is magnetorheological or electrorheological.
German patent specification DE 101 60 610 B4 discloses a filter for an X-ray examination apparatus for absorbing X-ray radiation having a plurality of controllable elements for generating electrical or magnetic fields that act on a liquid that absorbs X-ray radiation and result in a field-dependent, locally differing absorption behavior via the liquid surface. The form of at least one part of the elements is chosen depending on the form of an object to be examined by the examination apparatus.